A wide range of medical treatments have been previously developed using “endoluminal prostheses,” which term is herein intended to mean a medical device adapted for temporary or permanent implantation within a body lumen, including both naturally occurring or artificially made lumens. Examples of lumens in which endoluminal prostheses may be implanted include, without limitation: arteries such as those located within coronary, mesentery, peripheral (including, e.g., abdominal and thoracic aorta), or cerebral vasculature; veins; gastrointestinal tract; biliary tract; urethra; trachea; hepatic shunts; and fallopian tubes. Various types of endoluminal prostheses have also been developed, each providing a uniquely beneficial structure to modify the mechanics of the targeted luminal wall.
A number of vascular devices have been developed for replacing, supplementing or excluding portions of blood vessels. These vascular grafts may include but are not limited to endoluminal vascular prostheses and stent grafts, for example, aneurysm exclusion devices such as thoracic aortic aneurysm (“TAA”) devices that are used to exclude aneurysms and provide a prosthetic lumen for the flow of blood.
A very significant use for such endoluminal or vascular prostheses is in treating aneurysms. Vascular aneurysms are the result of abnormal dilation of a blood vessel, usually resulting from disease or a genetic predisposition, which can weaken the arterial wall and allow it to expand. While aneurysms can occur in any blood vessel, most occur in the aorta and peripheral arteries, and particularly the abdominal and thoracic aorta.
Aneurysms have been treated by implanting tubular prostheses within a body lumen to provide a lumen or lumens for blood flow while excluding blood flow to the aneurysm site. They are introduced into a body lumen using a catheter to place the endoluminal prosthesis at the diseased site within the body lumen. Many of the aneurysm exclusion devices are self-expanding and expand inside the body lumen as they are being released from the catheter. They typically securely engage a vessel wall above and below the aneurysm site to exclude the aneurysm site from the flow of blood.
Typically these endoluminal prostheses or stent grafts are constructed of graft materials such as woven polymer materials (e.g., Dacron, or expanded-polytetrafluoroethylene (“ePTFE”)) secured to the inner or outer diameter of a support structure including a plurality of annular members. The annular members provide sufficient radial force so that the prosthesis engages the inner lumen wall of the body lumen to hold the graft material in place against a lumen wall to exclude the flow of blood through the prosthetic lumen from the aneurysm.
The support structure in most endoluminal prostheses include some type of longitudinal support mechanisms, e.g., between annular supports structures. Longitudinal supports such as, e.g., a bar extending the length or a portion of the length of the graft have been used in a variety of different stent-grafts. Other types of longitudinal support may include, e.g., individual connecting elements between adjacent stent rings, or a fully supported stent structure (e.g., the AneuRx® stent graft). The longitudinal support mechanism provides columnar support when the device is loaded in a catheter, preventing kinking and wrinkling of the graft material when the device is deployed; and the support member further provides columnar support for the device when in place in vivo. However, such support mechanisms reduce the device flexibility when deployed, making it difficult to place the device in a particularly curved or tortuous vessel lumen. Furthermore, a stiff body such as that of a longitudinally supported prosthesis may be more prone to kink in a manner that leads to vessel occlusion. The columnar support elements hinder deliverability to some degree by presenting a stiffer catheter body. Also, the columnar support elements in many situations must be lined up in certain orientations making delivery more complex. Finally, the stresses on columnar support elements can cause them to fracture.
Accordingly, it would be desirable to provide a delivery system that eliminates the need for a longitudinal support member in deployment. It would also be desirable to eliminate device fatigue associated with longitudinal support members and subsequent breaks and fractures. It would also be desirable to provide a flexible endoluminal prosthesis for a more simplified deployment in curved or tortuous vessels. It would also be desirable to provide a delivery system and method for delivering a graft device that avoids wrinkling and kinking.
Mechanisms have been used in delivery systems to facilitate stent-graft delivery and reduce deployment force. For example, runners within the catheter along the outside of the prosthesis length have been used to reduce friction during deployment between the sheath and the prosthesis. The runners have been particularly useful where the support structures are located on the outside of the graft material and tend to engage the inner circumference of the sheath covering the prosthesis. However, the runners tend to be difficult to retract back into the catheter because after deployment they end up between the vessel wall and the expanded prosthesis. Furthermore, these mechanisms do not provide a means for reducing deployment force of a prosthesis having an unsupported portion.
It would also be desirable to provide a mechanism for reducing the force required to deploy a flexible or minimally supported prosthesis.